Balanced impulser circuit



Sept 20, 1960 o. F. GERKENSMHER 2,953,646

BALANCED IMFULSER CIRCUIT /Nl/E/VTOR 0f' GERKENSME/ER g MA' ATTORNEY United States Paten-tOiice 2,953,646 Patented Sept. 20, 1960 BALANCEDy IMPULSER CIRCUIT Otto F. Gerkensmeier, New `York,'N.Y., assignor to.Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York t -Filed Mar. 10, 1958, Ser. No. 720,497

4 Claims. (Cl. 179--16) This invention relates to transmission systems and more .particularlyfto panel call indicator .signaling systems.

vBrieily, in a panel call indicator system, digital information is conveyed from yan impulser circuit to areceiver circuit by transmitting pulses of varying current level-and polarity over interconnecting line conductors tofoperate sensitive polarized or marginal relays in the receiving circuit. As is well known in the art, the panel Ycallfindicatorfcode consists ofl various combinations of pulses of diierent'polarity andmagnitude, each combinaktion'representing a particular decimal digit `(see,for example, United'States Patent No. 1,438,743 whichissued to E. H. Clarkon December l2, 1922). Such a combination consists of four ksequentially tnansrnittedpulses, usually the lirst and third of which are either light positive-or so-called lblank pulses and the second yand fourth offwhich'are either light or heavy negative pulses.

It `has been found that present panel call indicator systems tend vto be unduly-susceptible to extraneous alternating-current voltages induced in the system line conductors. f When, for example, a light vnegative vpulse is transmitted insuch a system, it has Vbeen found 4that kan induced extraneous potential of as little as 6 volts (root mean square) can resultin malfunctioning of the sys- -tem receiving equipment.

It is` accordingly a principal object of this invention to Ieliminate theundesirable eiectsvof spurious `signals `that are induced in lthe line conductors of panel call'indicatorfsystems; that is, Yto veliminate lsignaling failures due-to these spurious signals.

In accordance Ywith the invention, various combinations of pulse-characterizing resistors for limitlngthe flow of the pulse current lover theline loop `are preselected and insertedin 'the loopby coordinated relay circuits Vso that -therloop isbalancedinsofar as longitudinal currents are concerned. -As will become apparent in the discussion vwhich follows, a panel call indicator signaling system Harranged in'accordance with this invention is1virtually, 'immu-neto alternating-current interference.

The invention will be understood more fully from the following more detailed description read in conjunction ifour quadrants or Vtime slots, as pulse positonsf are .often eallediin the electronics art. The lirst and third quadrants insuch a code are reserved for information in the iforrn of either so-called blank pulses (actually, these are not pulses -at'all)or light (relatively small in magnitude) positive pulses.

:pulses to be transmitted tothe receiver circuit 10.

The second and fourth v r systems.

.quadrants are used for transmitting information in the form of reither lightor .heavy (relatively large in magnitude) negative pulses. Thus, byusing various cornbinations Aof light positive, so-ealled blank, light negative, and heavy negative pulses, a numericalor stations code, for example, may easily be devised for the identiiication of parties in a panel call indicator signaling system. For a similar code, see the above-cited Clark patent.

It should be noted .at this point that ,light and heavy are relative terms, Whether a pulse will be light or heavy depends upon the'amount of resistance which is selectively inserted in the signaling system. Thus, various combinations of the resistors R1, R2, R3, R4, R5,"and R6 of Fig. .1 will cause light, heavy, or blank VIn Fig. l, the receiver circuit 10 has been shown in block form, ysince the description of its internal operation `is not necessary for present vpurposes and is well known .the type mentioned above.

The;signaling system of Fig. 1 may be a pm of, for

rexample, the crossbar telephone system disclosed in Patent No. 2,585,904 which issued to A. l. Busch on February 19, 1952. The transmission of pulses to the receiver `circuit '10 in proper quadrants is controlled by the steering and register circuit 12 which, in turn, operates in accordance with the particular intelligence to be transmitted. The steering and register circuit 12 is well knowntn the art and may be, for example, of the type disclosed in the above-cited Busch patenttsee Busch Figs. 221-through 226 and the section entitled Transfer of ACalled v'Line Number to Sender, beginning at page ,1117). Any intelligence to be transmitted over the tip conductor -16 `and the ring conductorlS is transmitted in theform of'a continuous train of pulse. groups. Each of thesepulse groups, as mentioned-above, consists of four time slots or quadrants.

*The oscillogram'of Fig. '2 illustrates how serious alterinating-current interference of relatively small potential canbe in panel `call indicator` signaling systems of the -typepresently-'us'edfl The solid trace is a lightpositive .tioning of sensitive relays(see, for example, the abovecitedV Clark patent) in the receiver circuit of prior art It is a feature of this invention that such a marked improvement in vdiscrimination against spurious Ysignals is obtained Vthat spurious voltages of as high as 7 5 volts rootmean square can lne-induced in the line conductors of afpanel call indicator signaling system with- "out any malfunctiorn'ng of Ithe receiver equipment.

;In^Fig. l the energization of relay No. II is controlled It will be seen that fthe energization ofrelay JN0. II is necessary fortheproduction of a lightpositive pulse, and that the deenergization 'ofthis relay isnecessuyfor ,the production. of a .blank pulse. Thus., .whetheralight positive` pulse or a .blank pulse is to be transmitted in the rstorthirdfquadrants .of a-anyipartieular pulse. groupndepends, respectively, alpen source of negative potential.

whether or not conductor 20 of steering and register circuit 12 is connected to ground.

The energization of relay No. I is controlled by steering and register circuit 1'2 via conductor 22. Conductor 22 is grounded at appropriate inteivals by circuit 112 in accordance with the message to be transmitted but may be grounded only during the second and fourth quadrants of any particular pulse group. It will be seen that the energization of relay No. I is a pre-requisite for the production of a heavy negative pulse and that the deenergization of this relay is a prerequisite for the production of a light negative pulse. Thus, whether a heavy or a l-ight negative pulse is to be transmitted in the second or fourth quadrants of any pulse group is dependent, respectively, on whether or not conductor 22 is connected to ground by steering and register circuit 12.

At this point it will be helpful to indicate the ele- Vments which must be inserted in series with the signal loop comprising the tip and ring conductors in order to produce the various types of pulses. Resistors R1, R2, R5, and R4 each have relatively large resistance values, while the resistance values of resistors R5 and R6 are relatively small. For purposes of this discussion, one source of negative potential is used throughout the illustrative embodiment.

For a blank pulse (first or third quadrant) the signal loop does not include the negative source of potential. No signal is transmitted by the impulser circuit to the receiver circuit 18. During the first small fraction of the blank pulse, the loop includes the resistor R5: (1) to decrease the dissipation of heavy pulse current in the contacts of relay No. IV, which current may have been manifest in the signal loop during the previous quadrant (second or fourth), and (2) to discharge residual energy stored in the capacity of the cable comprising ythe tip and ring conductors. The resistor R5 has a resistance value substantially less than that of the relay coil windings (not shown) of receiver circuit l so that the residual energy stored in the cable capacity will be discharged through resistor R5 rather than through the relays (not shown) of receiver circuit 10, since the latter might cause malfunctioning of the receiver equipment. During the remainder of the blank pulse the signal loop is open-circuited by the operation of relay No. III.

`For a light negative pulse (second or fourth quadrant), the signal loop includes the resistors R1 and R2 and the Resistor R1 is connected between ground and the tip conductor 16, while resistor R2 is connected between the ring ocnductor 18 and the source of negative potential. Because of the relatively large resistance value of the series combination of resistors R1 and R2, a negative pulse of relatively light potential is transmitted to the receiver circuit 10.

For a heavy negative pulse (second or fourth quadrant), the signal loop includes the source of operating potential and the relatively small resistor R5. The tip conductor 16 is connected directly to ground While resistor R5 is connected between the ring conductor 18 and the source of operating potential. Because of the relatively low impedance inserted in the signal loop by resistor R5, a negative pulse of relatively heavy 'potential is transmitted to the receiver circuit 10.

Finally, for a light positive pulse (rst or third quadrant), the signal loop includes the source of operating potential and the resistors R2 and R4. Resistor R4 interconnects ground with the ring conductor 18, while resistor R5 interconnects the tip conductor 16 and the source of operating potential. Because of the relatively large resistance value of the series combination of resistors R5 and R4, a positive pulse of relatively light potential is transmitted to the receiver circuit 10.

The manner in which the above elements are inserted in the signal loop to produce the various types of pulses will now be described.

Assuming that the pulse desired to be transmitted in the `first or third quadrant of a particular group is a light positive pulse, steering and register circuit 12 will energize relay No. II by connecting the negative source of potential to ground. Relay No. IV is energized only during the time duration of the first and third quadrants, that is during the periods of blank or light positive pulses. The timed interrupter circuit 24 cyclically energizes relay No. IV by completing the coil circuit of the relay to ground. Circuit 24 may be, for example, a resistance-capacitance-timed relay. Thus, when relay No. II is energized by steering and register circuit i12, relay No. IV is also energized by the timed interrupter circuit 24. A circuit is thereby completed from the impulser circuit to the receiver circuit 10 via t-ip and ring conductors 16 and 18. More specifically, the circuit includes resistor R4, contact 26 of relay No. II, contact '28 of relay No. IV, ring conductor 18, the coil windings (not shown) of the various relay circuits (not shown) in receiver circuit 10, tip conductor 16, contact 30 of relay No. IV, contact 32 of relay No. II and resistor R3. In accordance with an important feature of the invention, the resistance values of resistors R2 and R4 are substantially equal so that tip conductor 16 and ring conductor 18 are balanced with respect to longitudinal currents.

Assume now that a light negative pulse is desired to be transmitted over the signaling system of Fig. l. Light and heavy negative pulses, it will be recalled, are transmitted only in the second and fourth quadrants. During the second and fourth quadrants, relay No. IV is always deenergized, since this relay is energized by the interrupter circuit 24 only during the first and third quadrants. For ythe transmission of a light negative pulse, relay No. I is also deenergized as are relays Nos. Il and III. In other words, .the circuit condition required for the transmission of a light negative pulse is that which is shown in Fig. l, since all the relays are these shown in their deenergized state. The specific elements making up the signal loop during the transmission of a light negative pulse are Resistor R1, contact 34 of relay No. IV, tip conductor 16, the coil windings (not shown) of various relays in receiving circuit 10, ring conductor 18, contact 36 of relay No. IV, resistor R2, and the source of negative potential. In accordance with the invention, resistors R1 and R2 have substantially identical values of resistance so that the 4tip and ring conductors 16 and 18 are longitudinally balanced and the undesirable aiects of alternating-current interference on light positive pulses are virtually eliminated.

Assume now that it is desired to transmit a heavy negative pulse over the system of Fig. 1. Such a pulse may be transmitted only in the second and fourth quadrants. As mentioned in the case of the light negative pulse, relay No. IV is always deenergized during the second and fourth quadrants. In order to transmit the heavy negative pulse, relay No. I must be energized and this is accomplished by grounding conductor 22 via steering and register circuit 12. Another prerequisite for the transmission of a heavy negative pulse is that relay No. IV be deenergized. Now, tracing the circuit which is completed by the energization of relay No. I and deenergization of relay No. IV, it will be seen that this circuit includes contact 38 of relay No. I, contact 34 of relay No. IV, tip conductor 16, relay circuits (not shown) of receiver circuit 10, ring conductor 18, contact 36 of relay No. IV, and the parallel combination of resistors R5 and R2 interconnecting contact 36 of relay No. IV with the negative source of potential. It will be noted that the circuit thus traced is not longitudinally balanced in that lthe parallel combination of resistors R5 and R2 on the ring side of the `system has no counterpart on the tip side of the system. Thus, the heavy negative pulse circuit is unbalanced. This unbalance, however, is of negligible consequence, as it will be remembered that the resistance value of R5 (and even more so, the parallel combination of resistors R5 and R2) is relatively small. Because of this minor imbalance, an extremely large amount of a1- ternating-current interference is required before the heavy negative pulse is affected. As a result, the heavy pulse circuit completed by the energization of relay No. I and the deenergization of relay No. IV is virtually immune to alternating-current interference.

Assume now that it is desiredto transmit no pulse, i.e., a blank pulse, -to the receiver circuit 10. A blank pulse, it will be recalled, may be transmitted only in the rst and third quadrants. For the transmission of a blank pulse it will be noted that relay No. II must be deenergized and that relay No. IV must be energized. When these prerequisites are met, for a small fraction of the first part of the quadrant (rst or third), resistor Re is shunted across the tip and ring conductors. During this fraction of the quadrant resistor Re serves to discharge the cable capacity of the system. The charge on the cable capacity, if not otherwise controlled, tends to discharge through the receiving relays (not shown) of receiver circuit and to operate these relays falsely. Moreover, resistor R6 serves to decrease heavy pulse current (which may have been present in the previous quadrant) through the contacts of relay No. IV. When relay No. IV becomes energized, it will be noted that contact 40 is connected -to ground, thus completing the circuit including the negative source of potential and the windings of relay No. III. Upon completion of this circuit, relay No. III is designed to be energized after a predetermined time delay. Delay circuit 42 has been shown merely to illustrate this delay feature of relay No. III. It should be noted that the delay elements associated with relay No. II-I ordinarily do not comprise a separate entity as illustrated by delay circuit 46 but, rather, are an integral part of relay No. III.

After the predetermined time delay has lapsed, relay No. III becomes energized and contact 44 is opened. The tip and ring conductors are then open-circuited, since resistor R6 is no longer connected acrossthem.

The following enumerated values of circuit elements of the illustrative embodiment of the invention may be taken as typical:

Resistor R1 ohms-- 3200 Resistor R2 do 3200 Resistor R3 dn 3200 Resistor R4 do 3200 Resistor R5 do 115 Resistor R5 do 100 Approximate time delay of relay No. III

milliseconds-- Negative source of potential volts-- 48 sistors; a source of operating potential; first, second, third and fourth pulsing relays; means elfective when said relays are deenergized for connecting said tip conductor to ground through Said first resistor and for connecting said ring conductor to said source of potential through said second resistor; means effective when said second and fourth relays are energized for connecting said tip conductor to said source of potential through said third resistor and for connecting Said ring conductor to ground through said fourth resistor; means effective when said first relay is energized and said fourth relay is deenergized for connecting said tip conductor directly to ground and for connecting said ring conductor to said source of potential through said fth resistor; and means etfective when said second and third relays are deenergized and said fourth relay is energized for connecting said sixth resistor across said tip and ring conductors.

2. A signaling system in accordance with claim 1 in which said iir'st and second resistors have substantially identical values of resistance and said third and fourth resistors have substantially identical values of resistance.

3. A signaling System in accordance with claim l in which said first, second, third and fourth resistors have substantially identical values of resistance.

4. -In a telephone System, a signaling network comprising an impulser circuit and a receiver circuit interconnected by tip and ring conductors; said impulser circuit comprising: first, second, third, fourth, lifth, and sixth resistors; a source of operating potential; first, second, third, and fourth pulsing relays; a steering and register circuit for selectively operating said first and second relays; an interrupter circuit for cyclically energizing said fourth relay in synchronism with the energization or deenergization of said second relay, said third relay operating in response tothe operative condition of said fourth relay after a predetermined time interval; means effective when said relays are deenergized for connecting said tip conductor to ground through said first resistor and for connecting said ring conductor to said source of potential through said second resistor; means elective when said second and fourth relays are energized for connecting said tip conductor to said source of potential through said third resistor and for connecting said ring conductor to ground through said fourth resistor; means effective when said rst relay is energized and said fourth relay is deenergized for connecting said rtip conductor directly to ground and for connecting said ring conductor to said source of potential through said fth resistor; and means eifective when said second and third relays are deenergized and said fourth relay is energized for connecting said sixth resistor across said tip and ring conductors; said last-named means ceasing to be effective, to so connect said sixth resistor, when said third relay becomes energized in response to the energization of said fourth relay after said predetermined time interval, said tip and ring conductors being open-circuited when Said second relay is deenergized and said third and fourth relays are energized.

References Cited in the le of this patent UNITED STATES PATENTS 2,763,726 Weller Sept. 18, 1956 

